The present invention relates to a test circuit for testing the circuit making or circuit breaking capability of high voltage apparatus, in particular switches, by means of a high current circuit and a high voltage circuit respectively having a source for generating a large current and source for generating a high voltage. For some time, various test methods for testing the circuit making or breaking capabilty of high voltage apparatus at full voltage rating have been considered by the IEC. In the prior art methods, direct field test performances have proven to be insufficient. Therefore, the testing of the apparatus must be undertaken wht the help of so-called two-circuit switches by which both a high voltage circuit and a high current circuit are connected to the tested apparatus. A high current source in the high current circuit can comprise a high current generator, for example. As high voltage source in the high voltage circuit, it is possible to use a bank of capacitors or a test transformer, as described, for example, in the professional journal, Elektrie, Volume 31 (1977), pages 321 to 324.
In the apparatus for carrying out the above-mentioned test method, a spark gap performs the necessary function of isolating the high voltage circuit and the high current circuit from each other. After the switch to be tested has been preignited, the spark gap is actuated as fast as possible, so that the switch to be tested is loaded with the proper switching current. The spark gap thus serves as a high-speed switching element.
The ignition of such a spark gap can take place as described in West German Auslegeschrift No. 1,516,094, for example. In the test arrangement disclosed therein, a series connection of two capacitors and one auxiliary spark gap is connected in parallel with the auxiliary switch to be ignited by means of a capacitance which is small in comparison to the capacitance of the two capacitors. The two capacitors are charged by equal but opposite direct voltages and the voltage produced thereby is sufficient to ignite the auxiliary spark gap as well as the auxiliary switch to be ignited.
Further, West German Offenlegungsschrift No. 2,113,798 discloses a method for reigniting, for a short time, an electric arc between the contacts of a high voltage circuit-breaker by means of an explosive charge which drives a flow of ionized gas between the contacts, whereby at least one or both contacts or electrodes of the spark gap are ionized by the gas.
This previously described method is now indispensable in the case of a spark gap which is used as a high-speed switching element in a test circuit for high voltage apparatus, because the voltage over the spark gap after the preignition of the switch to be tested only amounts to the sum of the voltage of the high current circuit and the electric arc voltage of the switch to be tested. This voltage is generally substantially less than the voltage of the high voltage circuit.
For high voltage test circuits such as those described above, it is extremely difficult to produce spark gaps which features, on one hand, the required response accuracy and which are capable, on the other hand, of conducting the short-circuit current or switching-in test current, as the case may be, for a specified period of time. In addition, such spark gaps must be shunted after the tested response in order not to load them with the switching-in test current for an unnecessarily long period. For this purpose, a high voltage switch having suitable insulation is necessary. Further, the control of the testing procedure is time-consuming and the testing arrangement is relatively complicated owing to the above-mentioned required test circuit elements.